MOSCOW, Jan 27, 2015 (AFP) - The UN said Monday that a rocket attack that killed 30 people in a city in eastern Ukraine deliberately targeted civilians, as Russian President Vladimir Putin spurned Western calls to rein in a pro-Moscow insurgency.

A senior UN official told an emergency Security Council meeting that the deadly rocket barrage on the port city of Mariupol came from pro-Russian rebel-controlled territory and sought to strike a civilian population, in violation of international humanitarian law.

Putin earlier ridiculed the Ukrainian army as NATO's "foreign legion" after the Western alliance's NATO-Ukraine Commission met to discuss a surge in fighting that has led to a spate of civilian deaths and put pressure on Ukraine's troubled military.

Another 12 people were reported killed Monday, including seven Ukrainian soldiers, as Kiev accused the pro-Russian rebels of firing more than 100 times over the past day on both military positions and civilian areas.

Fighting was said to be particularly intense near the government-held city of Debaltseve, halfway between the rebel strongholds of Donetsk and Lugansk, where the military said separatists were attacking with tanks and multiple rocket launchers.

Western governments and Kiev accuse Moscow of arming, training and fighting alongside the rebels. Russia denies any direct involvement, although repeated sightings of large numbers of sophisticated heavy weapons being used against Ukrainian forces has stretched the credibility of those denials.

UN Under Secretary-General Jeffrey Feltman told the emergency Security Council meeting late Monday that a crater analysis by European monitors showed that the deadly rocket barrage was fired from territory controlled by pro-Moscow rebels.

"Mariupol lies outside of the immediate conflict zone. The conclusion can thus be drawn that the entity which fired these rockets knowingly targeted a civilian population," said Feltman.

"We must all send an unequivocal message: The perpetrators must be held accountable and brought to justice," he said.

'Cannon fodder'===================Putin, on a visit to Saint Petersburg, claimed Ukrainian men wanted to flee to Russia because they did not want to become "cannon fodder" in an army that he described as mostly "volunteer nationalist battalions".

"In essence, this is not an army, this is a foreign legion -- in this particular case NATO's foreign legion, which of course does not pursue the objective of serving Ukraine's national interests," Putin said.

He said the aim was "Russia's containment" and that the Ukrainian government was not interested in a peaceful settlement.

NATO head Jens Stoltenberg later dismissed the comments as "nonsense".

"The foreign forces in Ukraine are Russian," Stoltenberg told a press conference at the alliance's headquarters in Brussels. "So I think that is in a way the problem, that there are Russian forces in Ukraine and that Russia backs the separatists with equipment. And we have seen a substantial increase in the flow of equipment from Russia to the separatists in Ukraine."

The unravelling of a September truce deal has picked up pace in the past few days, with the main rebel leader in the Donetsk region last week announcing he would no longer take part in peace talks and planned to seize more territory.

Rebels distanced themselves from Saturday's rocket attack on a residential area of Mariupol, the last major city in the country's two separatist provinces still controlled by Kiev.

However, monitors from the Organization for Security and Co-operation in Europe said the rockets were fired from the direction of separatist-held areas.

The leader of the self-proclaimed Donetsk People's Republic, Alexander Zakharchenko, initially claimed Saturday to have launched an offensive aimed at taking Mariupol, but as the extent of the bloodshed became apparent he denied ordering an assault on the industrial port on the Sea of Azov. Mariupol remained calm on Monday.

More sanctions? ===================The 15-member UN Security council was meeting after Russia at the weekend blocked a statement condemning the violence in Mariupol and citing Zakharchenko's announcement of the offensive.

Russia is already under heavy Western sanctions over its alleged actions in Ukraine and the recent violence has led to threats of new measures against Moscow.

US President Barack Obama vowed to ramp up pressure on the Kremlin after Saturday's slaughter in Mariupol. Analysts say that if rebel forces did capture the city, they would then be close to creating a land corridor linking Russia to the Black Sea peninsula of Crimea, another Ukrainian province that Moscow annexed last March.

Obama said he would look at all options -- short of military intervention -- to restrain Putin's alleged campaign to cripple Ukraine's pro-Western leadership by stripping away their country's vital eastern industrial base.

In a call to Putin, French President Francois Hollande declared he was "very concerned" by the rise in violence and stressed the necessity for an immediate end to the aggression, a position shared by German Chancellor Angela Merkel, who was also on the call.

Ukrainian President Petro Poroshenko told his top generals that he had asked the European Union to tighten its own sanctions on Russia when EU foreign ministers hold a special session in Brussels on Thursday.

Both sides on the ground accuse the other of endangering civilians by firing into built-up areas.